The present invention relates generally to radio communications systems, and more specifically to 50-Watt radio frequency (RF) power amplifier systems used in military vehicle applications.
Constant gain (i.e., output power with respect to input power) in radio frequency (RF) communications is typically difficult to obtain because of several factors, including the wide frequency range (bandwidth) of the transmitted RF signals, effects (e.g., parasitic inductance, parasitic capacitance) of electronic components in the transmitter and amplifier portions of the communication system, temperature variations, shifts in tolerances, changes in the transmission medium, and device limitations, for example. Attempts to achieve constant gain have included complicated adaptive techniques, which are often difficult to calibrate and typically not robust over a wide range of conditions. An improved scheme for achieving constant gain, over a range of frequencies is desired.
In one embodiment, an apparatus for maintaining approximately constant gain of an output signal with respect to an input signal for an amplifier includes a digital control module. The digital control module is configured to determine a digital gain control value. The digital gain control value is determined in accordance with a selected frequency indicative of a carrier frequency of the output signal; a selected gain value indicative of a gain of the output signal with respect to the input signal; and predetermined calibration values indicative of an inherent closed-loop gain as a function of frequency of the amplifier. Parameters of the amplifier are adjusted in response to the digital gain control value to obtain approximately constant gain.
In another embodiment, a method for maintaining approximately constant gain of an output signal with respect to an input signal for an amplifier includes determining a digital gain control value and adjusting parameters of the amplifier responsive to the digital gain control value to obtain the approximately constant gain. The digital gain control value is determined in accordance with a selected frequency indicative of a carrier frequency of the output signal, a selected gain value indicative of a gain of said output signal with respect to the input signal, and predetermined calibration values indicative of an inherent closed-loop gain as a function of frequency of the amplifier.